docs: explain that layout height/width must be used to override include layouts

Change-Id: I7ee63f2f05b2e9a8cd424dfb2e7c9bead9d5efc6

docs/html/training/improving-layouts/reusing-layouts.jd

@@ -109,6 +109,10 @@ example:</p>
          layout=”@layout/title”/>
 </pre>
 
+<p>However, if you want to override layout attributes using
+the <code>&lt;include&gt;</code> tag, you must override both
+<code>android:layout_height</code> and <code>android:layout_width</code> in order for
+other layout attributes to take effect.</p>
 
 
 <h2 id="Merge">Use the &lt;merge&gt; Tag</h2>